CFTR doesn't allow fluids to clean the surface of the lungs that can cause deadly infections.

"The new treatment, Kalydeco, actually makes the protein work better," Accurso said.

It clears out the lungs, reduces symptoms, and possibly also prevents further damage to the lungs.

Caleb still has to use a machine to shake loose mucus in his lungs, but he's feeling healthier than ever before.

"To know that we have something that we give him now every day that's changing the way his body feels, correcting the underlying defect, there aren't any words for that," said Melissa Nolan, Caleb's mother.

Kalydeco currently is approved only for use by four percent of CF patients with a specific gene mutation. The U.S. Food and Drug Administration, however, has now fast-tracked Kalydeco-combination-treatments that may help up to 65 percent of cystic fibrosis patients in the near future.

The drug costs $300,000 a year, but almost all insurance companies will help with the cost.